The present invention relates to a security control technique for an electrically erasable programmable nonvolatile memory device in a semiconductor device including the nonvolatile memory device and a data processing technique of rewriting by externally changing the security state of the nonvolatile memory device in a data processing system incorporating the semiconductor device, and to a technique effective when applied to e.g. a microcomputer and its application system.
Japanese Unexamined Patent Publication No. 2004-213216 describes an information security microcomputer, which includes a cryptographic circuit for encoding and decoding information, an authentication program for authenticating an in-circuit emulator (ICE) proper, and a CPU for performing overall control of the information security microcomputer. If the authentication of the ICE proper is not confirmed, the CPU stops at least some functions of the information security microcomputer. Accordingly, an unauthorized person cannot use the information security microcomputer as an ICE microcomputer, which can improve the security.
Japanese Unexamined Patent Publication No. Hei 6 (1994)-35858 describes a control technique in which a password storage area and a security state memory area for storing either a locked state or an unlocked state are provided in an EEPROM of a terminal device, the security state transitions to the unlocked state upon storage of a password, the security state transitions to the locked state and a password input screen is displayed if the password is stored and a security lock is instructed, and a regular business screen is displayed in the unlocked state. In the state in which the password input screen is displayed, an input signal is checked against the stored password. If the input signal matches the password, the security state transitions to the unlocked state. The security state remains the locked state until a match is made.